MRAM (Magnetic Random Access Memory) is nonvolatile memory utilizing a magnetoresistive effect such as a TMR (Tunneling Magneto Resistive) effect, and is watched by all the world with keen interest as epoch-making next-generation memory having integrating density comparable to that of DRAM (Dynamic Random Access Memory) and high-speed characteristics comparable to those of SRAM (Static Random Access Memory), and capable of unlimitedly rewriting data.
A configuration of the MRAM is formed for example of and underlayer, a magnetoresistive film as a basic structure of a magnetoresistive element, and a cap layer, which are formed in sequence on a silicon or glass substrate having metal wiring (or a word line). As an example of the magnetoresistive film, an antiferromagnetic layer, a magnetization pinned layer, an insulating layer, and a magnetization free layer are stacked one on top of another in sequence from the underside.
The magnetoresistive element is placed for example at a point of intersection between a word line and a bit line for use in reading and writing of signals. The magnetoresistive element is used as a memory cell in which an underlayer of a lowermost layer and a cap layer of an uppermost layer of the magnetoresistive element are processed into a lower electrode and an upper electrode, respectively, which are then connected to wiring, thereby serving as electrodes.
The magnetoresistive element is configured such that reading or writing of data is performed by exchanging information with the metal wiring by changing an electrical resistance value of a current passing through the insulating layer to “0” or “1” by freely changing a direction of magnetization of the magnetization free layer by perpendicularly passing a current through the magnetoresistive element from the lower electrode to the upper electrode.
Etching technique is generally used to process the magnetoresistive element. The Etching technique includes IBE (Ion Beam Etching) method and RIE (Reactive Ion Etching) method.
It is known that, in the reactive ion etching method in particular, a metal film of the magnetoresistive element can be selectively etched by using a mixed gas of hydrocarbon said oxygen as an etching gas. (Refer to Patent Document 1.)